How to create a flare lighting up the background
Firstly, that sphere is not lighting up the background. The background appears to be an HDRI and the HDRI lights the scene, the scene does not light the HDRI. The effect that you want is glow (aka bloom).
If you are in Eevee then you can give that sphere an emission shader and turn on bloom. and that is the only step. If it does not appear change the emission value or change the values of the bloom.
If you are in Cycles there are two options (probably more, but these are what I know).
First way is to give it an emission shader set to any ammount and set the render passes to include Emission. Then in the compositor use a gleam node set to something like fog glow.
The second way is to render it twice (this is the slow method unless you have a good computer or little geometry). Render it once in Cycles for the high quality render and again in Eevee (at the same resolution and settings except maybe samples which can be turned down). In Eevee set the render passes to include bloom. In the compositor combine the Eevee bloom pass with the cycles render with a MixRGB node set to screen or add.